According to Nina Rees, the head of the National Alliance for Public Charter Schools, this proves that charters have become a viable academic alternative, especially in places where public schools have continually underperformed. As she put it in a quote in The Wall Street Journal, “if it can happen in Massachusetts, it can happen anywhere.”

Charter schools which are publicly funded but operate independently of the local school district are funded based on on the number of students they enroll. Because this is seen as a stripping money from public schools, the Massachusetts Teachers Association, the state’s arm of the American Federation of Teachers, is expected to oppose the move.

While some say capping the number of charter schools controls the quality of education, others say the caps are arbitrary and limit opportunity. Nationally, about 20 states have laws limiting the expansion of charter schools, according to the Center for Education Reform, a group that advocates for charter schools. Hawaii, Idaho and Missouri lifted caps last year.

There are 76 charters operating in the state at the moment, well under the 120 cap limit. But their growth is also restricted by the fact that districts are limited in how much of their funding they can spend on charters. State law caps the expenditure at 18% of total revenue in districts that chronically underperform and at 9% for those that don’t.

According to the groups supporting the expansion of charters, there are 45,000 students on various charter waiting lists throughout the state, although – according to the WSJ – that includes some that apply to multiple charters.

A coalition of charter advocates, charitable leaders and business groups—including the Pioneer Institute, a free-market Boston think tank—are pushing for the bill. But it has plenty of critics. The popular liberal Massachusetts blog Blue Mass Group wrote recently that Mr. Finegold “throws away his political future,” having “taken the lead for school privatization.”

Although the bill’s sponsors Senator Barry Finegold and Representative Russell Holmes are both Democrats, the bill’s passage is far from certain. The state’s Democratic Governor Deval Patrick – who supports charters – declined to comment on the measure.